This invention relates to a propeller for an outboard drive and more particularly to an improved exhaust system for the propulsion unit for an outboard drive.
In connection with outboard drives, such as the lower unit of an outboard motor, it has been the common practice to discharge a small amount of exhaust gases in proximity to the propeller blades to aerate the water around the blades. The reason for doing this is to decrease the viscosity of the water around the blades so as to reduce the drag resistance and permit rapid acceleration of the propeller. Although such arrangements provide for the desired result, they also have the tendency to reduce the viscosity of the water around the propeller when travelling at high speeds. Hence, there is a power loss that is attributed to this aeration when the boat is operating at high speeds.
It is, therefore, a principal object of this invention to provide an improved exhaust system for an outboard drive.
It is another object of the invention to provide an outboard drive exhaust system that aerates the propeller at low speeds to improve acceleration and which reduces the aeration at higher speeds so as to improve driving thrust.
It is a further object of this invention to provide an improved propeller, exhaust system for outboard drives.
It is another object of this invention to provide a propeller for an outboard drive that will introduce exhaust gases in proximity to the propeller blades at low speeds so as to aerate the blades and which will not provide this aeration when operating at higher speeds.